The present invention relates to a digital audio disc system in which an audio PCM signal is recorded as a geometrical pattern.
Conventionally, audio discs contain analog audio information recorded therein in the form of various undulation in a spiral groove. Such undulations are sensed by a stylus of a playback device, the stylus riding in the spiral groove and following the various undulations therein. Typically, the stylus is coupled to a magnetic sensor, or cartridge, whereby the mechanical motion of the stylus is converted to an electrical signal; and this electrical signal ultimately is converted into audible sound.
Recently, it has been proposed to digitize audio information, and to record the digital audio signals directly on a disc. The digital signals are sensed, or played back, by optical means such as a scanning laser beam. The produced digital signals then are re-converted back to audio signals which are used to generate corresponding sounds. Many advantages arise from the digital recording of audio information, such as markedly improved fidelity of the original audio signals, the ability to produce high-density digital audio discs which contain a larger quantity of information and thus permit relatively long playback times, and, since the playback "head" need not be in physical contact with the disc, the disc will be subjected to virtually no wear, and selected portions, or programs may be rapidly accessed for reproduction.
In digitizing the audio information to be recorded on the digital audio disc, it is pulse code modulated (PCM). To assure proper and desirable playback of such audio PCM signals, various synchronizing and control signals along with error correction code are also recorded on the disc, and such signals advantageously are multiplexed with the digital audio signals. The use of digital techniques enables at least some of the control signals to function as cue signals for use in controlling the playback device, editing equipment or the like. For example, the cue signals may represent the identity of the audio information program which is recorded, the length of that program, the number of programs recorded on a disc, the location of the beginning or end of that program, the composer, author or performers of that program, various movements of that program (particularly where such programs are musical performances), and the like.
As described above, a digital audio disc may have a main channel in which the main data consisting of audio PCM signals and a code for error correction are recorded and a subchannel in which various information digital signals other than the main data are recorded. In such a digital audio disc system, it is desirable to display such various information data on a display device so as to make known the various necessary information and to enable the simpler, easier and quick playback operation.
However, in a conventional digital audio disc system, there were many defects, such as, the display data lacks a part thereof; the display data is not displayed in the correct position; different contents are displayed on the screen simultaneously; the display data is displayed in fragments, and so on.
The indication of such abnormal display data mentioned above often occurs when the pickup device moves at a high speed in the radial direction on the disc in the search mode, or when the power of the system is turned on, or when the playback is not started precisely from the display start position, and the like.
There is also a defect that an extra display control unit must be prepared to prevent the indication of the abnormal display data, this causes a larger hardware for correct display data on the display device.